Differential microphone.



(P. 1. HACKETT. I DIFFERENTIAL MICROPHONE. APPLICATION FILED bCT. 23.I916.

1,274,035. I Patented July-30,1918.

Inna/7 6 7 cured. A'cone deflector '7 is integral 1 the said mouth piece6. v A series of per U ITED STATES PATENT oEEIoE.

PAUL J. AoKETnor sEATTLE, ASHINGTON, AssIerNoR TouNIvE nsAL HIGH POWERTELEPHONE COMPANY, or KING COUNTY, WASHINGTON.

DIFFERENTIAL MICROPHONE.

. Specification of Letters Patent.

Patented July 30, 1918.

Epplication filed October 23, 1916. Serial No. 127,109.

To all whom it may concern:

Be it known that I, PAUL J. HAGKETT, a citizen of the United States, anda resident of Seattle, in the county of King and State of ashington haveinvented certain new and useful Improvements in DifferentialMicrophones, of which the following is ra full, true, and exactspecification.

My invention relates to improvements in differential micropl'iones andhas for its principal object to improve upon the construction ofmicrophones and carbon cups as illustrated in my previous application,Serial No. 68,109, filed December 22nd, 1915, in that a carbon cup isprovided which is non-packing, airtight and therefore does notdeteriorate. Another object of my de- Vice'is to provide a simple andnovel construction which embodies a metallic diaphragm having carboncups adjustably secured oneon each side thereof. In microphones for highpower work attempts have been made to use carbon diaphragms but theexcessive breakage in thin carbon diaphragms of relatively largediameter. has

prevented their extensive use. The usual carbon cups give serioustrouble from packing of the carbon granules, due to excessive heat,absorption of moisture and lack offacilities for expansion. -The abovedisadvantages have been overcome in my device. Other objects Will appearas my invention is more fully explained in the following specifications,illustrated in the accompanying drawing and pointed out in the appendedclaims. I a

In the drawings Figure 1 is a plan view of my device. Fig. 2 is acentral cross section. of same. Fig. 3 is an enlarged cross sectionalView ofone of my carbon cups.

Referring more particularly to the drawings, numeral 1 indicates adiaphragm housing which has an annularring 2 integral therewith. Ametallic diaphragm 3 which is housed by a felt ring *1 rests within ring2 and against housing 1. The diaphragn 3 may be held in place by anyapproved cl-z ping means. The upper portion of hodsing 1 is providedwith a threaded mouth piece ring 5 within which the mouth piece is-seithhousing 1 and is centrally located within orations 8 are cut in thehousing between the cone deflector 7 and the mouth piece 6. A

cylindricalshell 9 extends downwardly-from housing 1 to a point close todiaphragm'3 and is of such diameter as to lie within the circle of holes8 A bridge 10 is secured toring 2 and crosses 'the'draphragm diametrically. A clamp block 11 is mounted uponbridge 10 and is insulatedtherefrom A pair of similar carboncups are mounted one on either side ofdiaphragm 3. One of the carbon cups fits within the cylindrical shell 9.Each of the cups is provided with a stem 12 one of which fits slida blywithin a cored opening' 18 in deflector 7 while-the other passesslidably through bridge 10 and block- 11. Each carbon cup mcludes a maincup 1a which is integral with ste n 12 andwhich is threaded internally.A carbon disk 15 is held in the bottom of cup 14 byme Y s of a threadednipple 16 which screws wit in cup 14. Nipple 16 extends beyond the openend of cup 14 and receives a threaded flange 17. A mica disk 18'is'clamped between the nipple and the threaded flange 17 .11 copperplated carbon disk 19 is' secured against the inside of mica diaphragm18 by means of a threaded rod 20 and a button 21. The outer ends of rods20 screw into a common nut 22 which is .used to connect the cups and-toclamp the diaphragm 3 between the nut and one of the buttons 21. Thespace within the carbon cups adjacent the inner surface of nipple 16 andthe mica disk 18. I fill with fiufiy asbestos which is held in place bysmall fragments and small threads being clamped between the ends of thenipple l6 and the carbon disk 15 and diaphragm 18. The remaining spacewithin the cup is filled with granular carbon, The presence of the'..flufl'y asbestos prevents packing of the carand scope of the invention,and I therefore desire to avoid being limited to the exact form shownand described. i

Having described my inv claim as nevviand dee're to t ters Patent, -is

1. The combination in a microphone which includes a dia )hragm ith aresilient lDSFr lating ring about its periphery and carbon cups(llSPOSBLl on opposite sides thereof, the movable electrodes of Whichare fixed to said diaphragm, of means for holding said diaphragm andcups in an ope ative position said means including a face plate threadedto receive a mouth piece, said face plate supporting the said diaphragmat its periphery, a conical shaped piece recessed to receive one of saidcups disposed at the center of said faceplate, there being aperturesthrough said face plate disposed about the base of said conical shapedpiece, said apertures communicating With the said mouth piece and beingadjacent the diaphragm, and a bridge attached to the back of said raceplate With an insulating lug thereon and bored out to receive another ofsaid cups.

2. In a 'niicrophonc having a pair of similar cups containing granulesof c-r;=n luctive mate 'ial, a movable diaphragm attached to said cupsin common, the combination in each of said cups of an internallythreaded main cup having a stem, a polished carbon disk Within thebottom of said internally threaded main cup, a threaded nipple withinsaid main cup and extending beyond the end thereofla micadiaphragmadjacent the outer end of said nipple, said mica diaphragmsupporting a movable electrode, said movable electrode including acarbon dish polished on its face and bored through the center to receivea stud Whose head is countersunk into the polished sln'ir'ace of thelast mentioned disk, said, stud passing through the said mica diaphragmand screwing through a back plate forming a support for the lastmentioned carbon disk, and the other surfaces of said carbon disk beingelectro-plated, a threaded flange screwed on the outer end of saidnipple and against said mica diaphragm, and a finfiy asbestos packingring Within said nipple and adjacent said mica diaphragm, whereby thegrani'dar conductive material contained Within the cup is allowed toexpand and packing is prevented. K

' PAUL J. HACKETT.

